[Cleanup] Gender constants cleanup (#3817)

* [Cleanup] Gender constants cleanup

# Notes
- Convert to a `Gender` namespace using `constexpr`.
- Cleanup spots where we were using magic numbers for gender values.

* Cleanup

zone/attack.cpp

@@ -5015,7 +5015,7 @@ void Mob::TryCriticalHit(Mob *defender, DamageHitInfo &hit, ExtraAttackOptions *
 				hit.damage_done = (hit.damage_done * SlayDmgBonus) / 100;
 
 				/* Female */
-				if (GetGender() == 1) {
+				if (GetGender() == Gender::Female) {
 					entity_list.FilteredMessageCloseString(
 						this, /* Sender */
 						false, /* Skip Sender */